1. Field of the Invention
The present invention relates to a remote steering system for remotely and hydraulically operating the outboard motor or engine and/or the rudder mainly of a small boat or watercraft. In particular, the invention relates to a system for remote steering with a single-rod cylinder, and to a hydraulic piston pump (also referred to as a helm pump) suitable for the system.
2. Description of Related Art
In general, as shown in FIGS. 7A and 7B of the accompanying drawings, a double rod cylinder 61 has conventionally been used for a remote steering system 60 of the type mentioned first herein. The cylinder 61 includes a body 61a fixed to the hull of a boat near the stern. The cylinder body 61a has an A port 61c and a B port 61d. The boat includes an outboard motor (not shown) mounted on the stern. The motor has a tiller 62 connected to one end of the piston rod 61b of the cylinder 61. The system 60 includes a steering wheel 63 and a manual hydraulic piston pump 70, which is mounted in the hull near the bow or stem. The pump 70 has an A port 71 and a B port 72, which are connected to hydraulic oil pipes 73 and 74, respectively. The other ends of the pipes 73 and 74 are connected to the cylinder ports 61d and 61c, respectively. As shown in FIG. 8 of the drawings, the hydraulic piston pump 70 may be a ball piston pump. In this case, the pump 70 includes a driving shaft 76, which can be turned with the steering wheel 63 (FIG. 7A). The pump 70 also includes a cylinder block 77, which can be turned with the shaft 76. The pump 70 has cylinders 78, in each of which a ball piston 79 can reciprocate. The pump 70 further includes a bearing type swash plate 80. The piston 79 is urged against the swash plate 80 by a spring 81. As the cylinder block 77 turns, the piston 79 can be pushed by the swash plate 80 to move axially in the associated cylinder 78 against the force of the spring 81. The pump 70 still further includes a distributing valve 82. As shown in FIG. 9B of the drawings, the valve 82 has an A port 83 and a B port 84. While the ball pistons 79 of the pump 70 are moving, pressure oil is discharged through one of the valve ports 83 and 84 (for example, the A port 83) into the associated port 61c or 61d (for example, the B port 61d) of the double rod cylinder 61, and pressure oil is sucked from the other cylinder port 61c or 61d through the other valve port 83 or 84 into the pump 70. This moves the piston rod 61b in the direction opposite to the direction in which the wheel 63 turns, thereby changing the direction in which the boat moves. In both directions in which the wheel 63 turns, the distances over which the rod 61b moves are equal to each other and proportional to the number of revolutions of the wheel 63.
The pump 70 may, in place of such a hydraulic pump of the ball piston and side plate type, be a hydraulic pump of the plunger and pintle type.
The inner side of the pump swash plate 80, which is in contact with the pistons 79, is a flat surface. As shown in FIG. 9B, the valve ports 83 and 84 are circular or arcuate and laterally symmetric. Accordingly, when one of the cylinders 78 turns by an angle of 360 degrees, as shown in FIG. 9A, the strokes of the associated piston 79 are equal on both sides of the angular position of the cylinder 78 at 180 degrees.
The free end of the piston rod 61b protrudes from the cylinder body 61a, and may interfere with the hull.
FIGS. 6A and 6B of the drawings show a remote steering system 30 with a single rod cylinder 31. This cylinder 31 includes a body 31a and a piston rod 31b. Only one end of the rod 31b protrudes from the cylinder body 31a, and is connected to the tiller 62 of an outboard motor, which is mounted on the hull A of a boat. Therefore, the rod 31b does not interfere with the hull. Besides, only a small space is necessary for mounting the cylinder 31.
As apparent from FIG. 6B, the amount of pressure oil necessary for moving the piston rod 31b to the right is smaller by the volume of part of the rod than that necessary for moving it to the left. For instance, six revolutions of the steering wheel 40 are necessary for moving the rod 31b over the whole stroke to the left, and three revolutions are necessary for moving it over the whole stroke to the right. Therefore, when the tiller 62 is turned from its neutral position to steer the boat, the rudder angle corresponding to a particular number of revolutions of the wheel 40 which is necessary for steering the boat to the right differs from that corresponding to the same number of revolutions for steering it to the left. Consequently, the operation of the wheel 40 is very difficult and needs skill.